Stirring mill

ABSTRACT

Stirring mill for homogenizing, dispersing and comminuting solids in liquids comprising an upright milling container or housing filled with grinding bodies 0.2 to 3 mm. in size in which a rapidly rotating stirring device is arranged and the material being ground is forced into the container from the bottom and leaves it by way of a separating device through the upper end, where the material being ground accumulates in a back pressure chamber defined by a cylindrical screen and a top element, where the outlet is above the cylindrical screen and the shaft of the stirring device is devoid of stirring elements in the area of the back pressure chamber and guide members are provided in the back pressure chamber which delay the movement of the grinding bodies and material being ground.

United States Patent Engels Feb. 8, 1972 [54] STIRRING MILL [72] Inventor: Kaspar Engels, Mannheim, Gennany [73] Assignee: Draiswerke Gmblll, Mannheim-Waldhof,

Germany [22] Filed: Jan. 13, 1970 [2]] App]. No: 2,485

[30] Foreign Application Priority Data Jan. 14, 1969 Germany ..P 19 01 593.1

[52] US. Cl ..241/74, 241/172 [51] Int. Cl. ..B02c 17/16 [58] Field ofSearch ..241/50, 46.15, 46.17, 74, 98,

FOREIGN PATENTS OR APPLICATIONS 1,254,944 1 H1967 Germany ..241/74 1,254,439 1 H1967 Germany ..241/74 Primary Examiner-Robert L. Spruill Attorney-Robert H. Jacob [57] ABSTRACT Stirring mill for homogenizing, dispersing and comminuting solids in liquids comprising an upright milling container or housing filled with grinding bodies 0.2 to 3 mm. in size in which a rapidly rotating stirring device is arranged and the material being ground is forced into the container from the bottom and leaves it by way of a separating device through the upper end, where the material being ground accumulates in a back pressure chamber defined by a cylindrical screen and a top element, where the outlet is above the cylindrical screen and the shaft of the stirring device is devoid of stirring elements in the area of the back presure chamber and guide members are provided in the back pressure chamber which delay the movement of the grinding bodies and material being ground.

7 Claims, 4 Drawing Figures srnuuno MILL BACKGROUND OF THE INVENTION The present invention relates to stirring mills of the upright type. More in particular the invention concerns stirring mills of the type used for homogenizing, dispersing and comminuting solids in liquids.

Stirring mills used for this purpose comprise an upright milling container or housing in which a rapidly rotating stirring mechanism is disposed. In addition, small auxiliary grinding bodies having a diameter of about 0.2 to 3 mm. are located in the grinding container into which the material to be ground is charged from the bottom by means of a pump. At the upper end of the grinding container at separating device, preferably a screen, is provided for the purpose of holding back in the container the auxiliary grinding bodies at the outlet for the material that is being ground.

SUMMARY OF THE INVENTION It is an object of the invention to further improve stirring mills of this type in a manner to prevent the formation of lumps in any event and to improve the grinding effect.

Accordingly the invention provides in a stirring mill of the aforementioned type that before the material being ground reaches an outlet it accumulates in a back pressure chamber defined by a cylindrical screen arranged above the grinding container and a top structure or element, where the outlet is above the cylindrical screen and the stirring shaft in the area of the back pressure chamber is devoid of stirring elements or arms, and guiding elements are provided in the back pressure chamber which delay the movement of the grinding bodies and of the material being ground.

In connection with the invention it was discovered that it is sufficient, in order to achieve the optimum grinding effect, if the excess pressure in the grinding container during working operations is only a small amount above the atmospheric pressure prevailing on the outside, and therefore provisions were made that above the separating means there is a back pressure extension or top, which is in communication with the outer air, into which the material can enter at variable height of its liquid level depending on its characteristics. Thereupon it becomes possible by means of the back pressure top structure to maintain sufficient pressure in the grinding container which is capable to effectively limit the lump formation in the grinding container that is known to be cumbersome, the undesired admixture of air and any possible developing foam formation, any premature freeing of light components of the material being ground, and the like. With the arrangement of the back pressure top above the operating space of the stirring mill, and due to the fact that the stirring mill shaft is devoid of stirring with respect in the area of the back pressure top, there results a safeguard against overflow of the may be container, and it is possible to extensively prevent the formation of lumps with its disadvantageous effects.

The guiding elements arranged within the cylindrical screen in the back pressure top brake the mixing of grinding bodies and material being ground that are moved by the stirring elements and the stirring shaft and guide them, preferably along spiral paths, from the intensively moving stirring shaft area outwardly to the calmer zone of the screen wall. In an advantageous embodiment of the invention the guiding members are arranged in the direction of rotation of the stirring mechanism tangentially with respect to the stirring mechanism shaft and are designed in the manner of guiding paddles. The guiding elements may be secured to a ring that can be suspended in the back pressure space or, for example, on a tubular top seated preferably at points on the cylindrical screen.

In accordance with a modified embodiment the guiding members may also be in the form of helically shaped guiding paddles. In accordance with a further feature of the invention the ends of the guiding elements proximate the shaft of the stirring mill are to be at a distance which corresponds to at least one or two times the diameter of the largest grinding bodies introduced.

BRIEF DESCRIPTION OF THE DRAWINGS Further details and advantageous features of the invention are explained hereinafter with reference to the drawing, in which FIG. 1 is a stirring shaft mill that has a cylindrical screen as a separating device, a back pressure top and in the back pressure chamber thus formed guiding members in accordance with the invention for avoiding lump formation,

FIG. 2 is a section taken along line I--I in FIG. 1,

FIG. 3 is a top plan view of a stirring mill with helically shaped guiding paddles arranged in the back pressure chamber, and

FIG. 4 is a detail in section showing the helical guiding paddles.

THE INVENTION The stirring mill illustrated in the drawing comprises a grinding container 1 which is provided with a mantle 2 for cooling or heating. In the grinding container the rapidly rotating shaft 3 has stirring elements 4. The separating device in the form of a cylindrical screen for separating the material being ground from the grinding bodies is indicated at 5. Above the working space 12 in the stirring mill which contains grinding bodies 16 a back pressure top structure 6 is arranged. The catching space 7 has an outlet or discharge stub 8 whose lower discharge edge is located at the level of the upper border 9 of the screen 5. It is possible to change the discharge height of the outlet stub 8 whereby the back pressure can be controlled. The stirring shaft 3 is devoid of stirring members in the area of the cylindrical screen and of the back pressure top 6. This space constitutes the back pressure space or chamber 13.

In the embodiment shown an upper open tubular member 6' is connected to the top of the cylindrical screen 5, the diameter of which corresponds to the diameter of the grinding container l in the embodiment illustrated.

In the back pressure chamber 13 guiding members 10 are disposed within the separating means 5, which are in the form of guiding paddles 11 in the embodiment in accordance with FIG. 1. The securing of the guiding members in the stirring mill may be obtained in different fashion. It is possible to arrange the guiding members on a ring 15 by means of hooks I7 that can be suspended in the back pressure chamber, or for example on the tubular portion 6.

As shown in FIG. 2, the guiding paddles 11 as seen in the direction of rotation of shaft 3 are arranged tangentially with respect to the stirring shaft. The guiding paddles on the one hand brake the movement of the grinding bodies and grinding material and, on the other hand, direct them from the circular path to a spiral path that leads to the cylindrical screen. In this manner a calming of the grinding body and grinding material mixture in the back pressure space 13 is obtained and lump formation, particularly also in the proximate area of the stirring shaft, is prevented. In order to avoid friction as well as destruction of grinding bodies between the grinding shaft and the guiding members and to take care of a transfer into the flow of the material being ground, the guiding elements are arranged at a minimum distance of approximately twice the diameter of the grinding bodies from the shaft.

The axial length of the guiding members 10 or guiding paddles 11 corresponds preferably to the height of the cylindrical screen. It has been found to be advantageous that the guiding paddles still extend somewhat into the working space. A further advantage is obtained if, beginning in the area of the upper edge of the screen, the guiding bodies maintain an increasing distance to the wall of the screen, which at the lower end of the guiding members may correspond to the distance of the wall of the stirring elements. Thus, an easier separation of the grinding bodies from the material being ground is obtained, because the grinding bodies canl wipe over a large part of the screen surface while whirling. The minimum distance of the guiding members from the screen wall should correspond approximately to one to two times the grinding body diameter of the largest grinding bodies in the mill. With the guiding paddie shape shown in FIG. 1 the distance of the paddles from the shaft is the same, while, beginning with the upper one-third, the distance relative to the cylindrical screen increases downwardly.

The guiding bodies 14 illustrated in FIG. 3 are guiding paddles that are helically shaped. These guiding bodies counteract particularly advantageously any lump formation. The invention is not limited to the guiding member shapes described. Depending on the material being ground, the most advantageous shape of guiding members can be chosen. Furthermore, the guiding members may be in the form of exchangeable inserts.

I claim:

l. Stirring mill for homogenizing, dispersing and comminuting solid substances in liquids, comprising an upright grinding container in which material to be ground is-forced in through the bottom and leaves through a separating arrangement at the upper end, grinding bodies between 0.2 to 3 mm. in size disposed in said container, a rapidly running stirring mechanism arranged in said container, a cylindrical screen disposed at the upper end of said container and a top container structure superimposed on said container around said screen defining a back pressure chamber with said screen, an outlet arranged in said top structure above the upper end of said screen, where material being ground accumulates in said back pressure chamber prior to discharge through said outlet, said stirring mechanism having a shaft devoid of stirring arms in the area of said back pressure chamber, and stationary guiding elements extending in said back pressure chamber for delaying the movement of said grinding bodies and of material being ground.

2. Stirring mill in accordance with claim 1, where said guiding elements are paddles extending tangentially to said shaft as seen in the direction of rotation.

3. Stirring mill in accordance'with claim 1, where said guiding elements are in the form of helically shaped guiding paddles.

4. Stirring mill in accordance with claim 1, where said guiding elements are spaced from said shaft by a distance corresponding to at least one to two times the size of said grinding bodies.

5. Stirring mill in accordance with claim I, where said guiding elements and said cylindrical screen define a gap therebetween of a size corresponding to at least one to two times the size of said grinding bodies.

6. Stirring mill in accordance with claim 1, where the axial length of said guiding elements corresponds substantially to the height of said cylindrical screen.

7. Stirring mill in accordance with claim 1, where the distance of said guiding elements from said cylindrical screen decreases upwardly and remains substantially the same in the area of the upper one-third of the height of the guiding elements. 

1. Stirring mill for homogenizing, dispersing and comminuting solid substances in liquids, comprising an upright grinding container in which material to be ground is forced in through the bottom and leaves through a separating arrangement at the upper end, grinding bodies between 0.2 to 3 mm. in size disposed in said container, a rapidly running stirring mechanism arranged in said container, a cylindrical screen disposed at the upper end of said container and a top container structure superimposed on said container around said screen defining a back pressure chamber with said screen, an outlet arranged in said top structure above the upper end of said screen, where material being ground accumulates in said back pressure chamber prior to discharge through said outlet, said stirring mechanism having a shaft devoid of stirring arms in the area of said back pressure chamber, and stationary guiding elements extending in said back pressure chamber for delaying the movement of said grinding bodies and of material being ground.
 2. Stirring mill in accordance with claim 1, where said guiding elements are paddles extending tangentially to said shaft as seen in the direction of rotation.
 3. Stirring mill in accordance with claim 1, where said guiding elements are in the form of helically shaped guiding paddles.
 4. Stirring mill in accordance with claim 1, where said guiding elements are spaced from said shaft by a distance corresponding to at least one to two times the size of said grinding bodies.
 5. Stirring mill in accordance with claim 1, where said guiding elements and said cylindrical screen define a gap therebetween of a size corresponding to at least one to two times the size of said grinding bodies.
 6. Stirring mill in accordance with claim 1, where the axial length of said guiding elements corresponds substantially to the height of said cylindrical screen.
 7. Stirring mill in accordance with claim 1, where the distance of said guiding elements from said cylindrical screen decreases upwardly and remains substantially the same in the area of the upper one-third of the height of the guiding elements. 